At the University of Wisconsin - Madison, we frequently have courses with over 500 students. With those numbers, we frequently get two students with the same name. When you're working in the gradebook, or in Speedgrader, there is no way to confirm which student is which.
Additionally, with a large population of foreign nationals, many will adopt Americanized names (e.g. "Frank", in lieu of "Zhang").
For these two reasons, (and there may be others) I would like to see a "Nickname" option for each student. A field (my thinking) in gradebook that could be toggled on/off as needed. Once the field is on, it is left blank for the all students. But, the instructor can custom populate that field for each student. Whatever is shown there would be used "in place" of the student's official name within the Gradebook, or SpeedGrader. If this field is left blank, then the official student name is employed as-is.